Oil burning furnace



Jan. 1, 1963 R. c. WRIGHT 3,071,181

' onJ BURNING FURNACE Filed Oct. 16, 1958 United States Patent O 3,071,18l GIL BURNING FURNACE Richard C. Wright, Bay Village, Ghio, assigner to Iron Fireman Manufacturing Company, a corporation of Gregori Filed Get. 16, 1958, Ser. No. 767,585 1 Claim. (Cl. 15S-4) This invention relates generally to residential heating equipment of the fluid fuel burning type and more particularly to fluid fuel burning equipment using mechanical induced draft apparatus for controlling the supply of combustion air to the burner and the mixing of the combustion air with the fuel as required.

Generally speaking it has been found that the same improved efficiency and reliability of performance is experienced when burning fuel gas in the manner of this invention as is found when burning oil but to avoid confusion the present disclosure is of oil burning equipment.

It is a principal object of this invention to provide in a fluid fuel burner means for controlling the mixture of the combustion air and fuel at a desired ratio not only during the normal running time of the burner but also during the starting and warming up time of the burner.

It is a second object to provide a fluid fuel burner which is clean and quiet in operation.

It is a third object to provide such a burner in which there is a substantial negative gas pressure within the combustion chamber at all times during the operation thereof.

It is a fourth object to provide such a burner in which the gas pressure within the combustion chamber is maintained sufficiently low to cause the combustion air to enter the combustion chamber at a speed of from 2500 to 3500 feet per minute.

It is well known that every pound of fluid fuel requires for perfect combustion a definite weight of air and that, practically, some excess air is required to be sure that all of the fuel is mixed with air within the combustion space of the furnace.

It is also well known that the -whirling spray type of oil burner nozzle as commonly used on residential pressure atomizing types of oil burners is made with a relatively large outlet orifice leading from a small whirling chamber into which the oil is directed by a plurality of relatively small whirling slots or tangentially directed oil passages. Due to this construction the amount of Whirl of oil in the whirling chamber materially affects the amount of resistance offered by the nozzle to oil flow therethrough. In other words the oil flow through a given nozzle when starting cold at a given pressure across the nozzle may be ten percent greater than the flow of oil through the nozzle after the burner is up to normal operating temperature. To prevent excessive smoke during the starting up period forced draft burners of the types commonly used are required to use air on starting greatly in excess of that required for normal running and since there is no simple mechanical way of adjusting the combustion air supplied to the burner the forced draft "ice ratio to the oil supply rate is to place the fan at a place in the combustion air stream where the air will be cold when the oil is cold and where the temperature of the combustion products through the fan rises as the oil temperature rises due to reflected heat yfrom the combustion chamber on the nozzle.

It is therefore an important fifth object of this invention to provide a pressure atomizing type of domestic burner with a combustion air supply fan at a position along the air stream' through the combustion chamber with which the burner is used at which the air will be cold when the oil is cold at the start of burner operation and at which the specific volume of combustion air and combustion products will increase due to increase in temperature and reduce the supply of combustion air at subsfantially the same rate at which the oil supply is reduced as the oil increases in temperature.

It is well known that air jetted at a relatively high velocity into a relatively quiet body of air generally causes noise and uncontrolled stratification in the .air-fuel mixture. Yet when the air is induced through an orifice by so lowering the pressure on the low pressure side of the jet that the air into which the orifice discharges is moving with substantial velocity away from the jet orifice then the air is jetted from the orifice smoothly and with complete control of its pattern of movement as it leaves the vicinity of the orice. I have found this to be a very much desired condition for the combustion air whirling envelope surrounding and mixing with the cone of atomized fuel discharging into the combustion chamber of a pressure atomizing oil burner.

It is therefore a sixth object to provide such a burner with means continuously maintaining in the combustion zone in the direction of flame travel from the burner a combustion gas pressure materially lower than the pressure of the air at its discharge from the air cone of the burner.

Contrary to the previous practice of designing a burner structure to promote turbulence in the combustion chamber at the location of meeting of the whirling air and whirling oil and the consequent requirement of supplying a great amount of excess air to the burner I have found that a relatively small amount of excess air is required if the air is mixed with the oil spray smoothly and without turbulence by the method of using an air discharge cone for the burner which expands in the same direction and approximately parallel to the conical oil spray from the burner and to provide a plurality of small slots through the air cone from the inside of the draft tube of the burner to the oil spray side of the air cone. I have discovered that the small air supply slots should be long in the expansion direction of the cone and narrow and equally spaced in the direction of the circumference of the cone, with the slots tipped in the direction of the whirl of the oil spray and with the slots small enough to emit the required combustion air into the space closely surrounding the cone of oil spray at a speed of from about 2500 to 3500 feet per minute.

It is therefore a seventh object to provide such a burner with an air discharge cone concentric with and within the draft tube of the burner at the outlet end thereof and expanding in the outlet direction of the tube; the cone having a disk with a central hole therethrough truncating the cone at its smallerl end and a plurality of air holes spaced over the sloping surface of the cone, the holes being circumferentially tipped to cause the air to leave the slots in the direction of whirl of the oil spray and inwardly toward said oil spray -at a rate of emission of the air from the holes of between about 2500 and 3500 feet per minute.

How these and other objects are attained is explained by the following description referring to the attached drawing in which FIG. 1 is a Afragrnental side elevation view in partial section of a forced air Vresidential space heating furnace the application to which of the burner of my invention is a feature thereof.

FIG. Z is an enlarged fragmental side elevation View in partial section of the burning head end of my unique oil burner shown in FIG. l.

FIG. 3 is an end elevation view along the line 3--3 of FIG. 2.

tFlG. 4 is a fragmental sectional view along the line 4-4 of FIG. 2.

Like reference numerals refer to like parts in the several figures of the drawing.

Referring now to the drawing there is shown resting on `floor 9 a forced warm air residential type furnace 10 having a furnace body 11 with a primary radiation combustion chamber vertical drum 12, connected yby a combustion gas conduit 13 to a hollow torus shaped second radiator -14 connected by a second combustion gas conduit 15 to a somewhat rectangular hollow tertiary radiator 16 having an outlet elbow 17 discharging to a stack 18 for discharging the combustion gases to atmosphere.

Completely surrounding the furnace body 11 and spaced therefrom is a furnace casing 26 rectangular in plan and equipped with access doors, not shown, to the interior thereof. The interior Vof casing 20 is divided by upright transverse barriers 21, 2.2 into a downward iiow cold air space 23, an upward flow warm air space 24 and burner and control space 25. Space air circulating fan 26 driven by-electric motor 27 draws air from the space to be heated through ducts, not shown, to the top Vopening 2S in cold air space 23 through porous air .cleaner 29 to the side opening 30 into fan 26 from where the air is ejected through opening 31 into warm air space 24 where the air is forced over the heated surfaces of ybody 11, out the warm air outlet 32 'from space 24- and through warm air ducts, not shown, to the space to be heated.

The interior of combustion drum 12 is connected near its bottom with space 25 by tube 78 welded at its respective ends as shown to the peripheries of holes formed in the Wall of drum 12 and through barrier 22.

IOil burner firing head 33, shown in more enlarged detail in FIGS. 2, 3 and 4, is shown in FIG. l to be secured by screws 34 to barrier 22 with the forward extension 36 of draft tube 35 of head 33 extending loosely through tube 78 and through a hole 37 formed through vthe side wall of ceramic lining 38 of the bottom of drum 1- Fuel supply motor 39 is seen in FIG. l to be provided with extensions of its shaft at either end thereof; to carry on one shaft end extension the induced draft fan wheel 49 and on the other shaft end extension the impellers, not shown, of the fuel control unit 41 the body -of which is securely supported on the frame of motor 39 by screws, not shown. The frame of motor 39 with fan 40 and fuel unit 41 is secured to dished flange 42 which in turn is secured, as shown, to barrier 22 and radiator 16 by screws `43 to cover holes, as shown, formed through barrier 22 and radiator 16 for the insertion or removal of fan 40 into or from `its position, as shown, in radiator 16.

Connected to fuel unit 41 is a fuel oil inlet conduit 44 leading from a storage source of fuel oil, not shown. A burner fuel supply conduit 45 `connects the outlet 46 of fuel unit 41 to solenoid operated delay starting and instant stopping oil valve 47 which when energized but after a time delay connects conduit 45 with nozzle pipe 48 of burner head 53. When the solenoid operator of valve 47 is de-energized the valve instantaneously cuts pipe 48 operatively from conduit 45. Fuel unit 41 is of a type well known in the art having a first pump for pulling oil from a source to the unit and a second pump for supplying oil under pressure to the fuel burner nozzle 49 at the outlet end of nozzle adapter 59 secured to the end of nozzle pipe 48. Unit 41 -also includes an oil strainer, a first preset valve allowing oil flow to conduit 45 only when the oil pressure is up to a desired figure, and a second preset valve adapted to by-pass oil around the second pump to its inlet side when the pressure in conduit 45 reaches a higher desired figure.

Draft tube 35 of burner head 33 is provided with an outside flange 51 secured tightly thereon to support the entire burner head on barrier 22 by screws 34 as above noted; additional flange 51a enters snugly into the opening of tube 78 to align draft tube 35 -concentrically therewith. Draft tube 35 is covered at its outer end by cap 52 secured thereon by screws 53, as shown. Set screw 53a set into sleeve 54 secured into cap 52 longitudinally positions nozzle pipe 43 therein. Nozzle adapter 50 is `formed on its outside like a hexagonal nut on its end vthreaded onto pipe 4S. On its other end nozzle adapter 50 is cylindrically formed and carries on its outer surface a tricorn centering sleeve 55 the three equally circumferentially spaced horns 56 of which accurately center `nozzle 49 in draft tube 35. Nozzle 49 threaded into the end of adapter 50 secures sleeve 55 in place.

Nozzle 49 is a pressure atomizing whirling spray type of nozzle for supplying fuel oil to a furnace burning distillate oil. Nozzles of this type, satisfactory for thi-s purpose, include many that accomplish the same result although each may vary in features of manufacturing design.

Air control cone 57 coaxial with extension 36 of draft .tube 35 is seen to be coaxial with nozzle 49 and to he Secured around the periphery of its open larger end to the interior of extension 36. The smaller end of cone 57 is seen to be cutoff and fitted perpendicularly to its axis with a disk 58 having a central hole 59 therethrough for the purpose of directing a proportion of the ycombustion air inwardly into the whirling oil spray from nozzle 49 and for directing into the oil vapor the spark from electrodes 59, 69 connected inside porcelain insulators 61, 62 to high voltage insulated wires 63, 64, one shown, leading from an ignition transformer, not shown.

In the sloping surface of cone 57 a plurality of equally circumferentially spaced triangular cuts are made substantially tangential to the outer edge of disk 58. In each position a second cut is made outwardly in the surface of the case from the greater diameter end of the first cut to a point in a plane including the axis of the cone and the other end of vthe first cut. Then each of the tabs formed in the respective positions are pushed into the cone to bend along the line of the non-adjacent ends of the two cuts, thus to form in the several positions a series of air slots `65 with air directing wings 66 for the purpose of admitting 4air `spirally axially and inwardly through the conical surface of cone 57. As shown in FIG. 3 the wings 66 are formed to whirl the air in the direction of arrows 67 which is the same as the whirling direction of the oil spray from nozzle 49' as shown by arrows 68.

It is particularly to be noted that cone 57 expands in the direction of fuel and air travel into the combustion chamber.

Air for combustion is admitted into draft tube 35 through a series of holes `69 in the wall thereof, the holes being adjustably covered by band damper 7d formed with holes 71 variably mating with holes 69 as damper "70v is moved circumferentially about draft tube 35.

Supporting bar 72 is formed with three transversely spaced holes therethrough to receive horizontally spaced therein nozzle pipe 48 in the middle hole and electrode insulators 61, 62 in holes on either side of pipe 48. An individual screw 73 is provided to secure each of pipe 48 and insulators 61, 62 in their positions found to set electrode ends 59, 6d and nozzle end 49 in their position .5 selected for best operation of the burner. Holes formed through cap 52 of draft tube 35 receive electrode insulators 61, 62 for their longitudinally adjustable support.

Cylindrical sleeve 74 secured to ange 51 as shown provides a protective cover over damper 7G and the associated air openings into draft tube 35.

In FIG. l an oil burner primary safety control 75 is shown to have a heat resisting tube secured by a flange to barrier Z2. The combustion temperature sensitive element extends through the tube and liange into tube 79 welded at its respective ends as shown to Vthe peripheries of holes formed in die wall of drum l2 and through barrier 22. Batiie 80 additionally protects the heat vulnerable parts of the control from the radiant heat of the furnace.

in addition to circulating air motor 27, `fuel supply motor 39, solenoid valve 47, primary safety control 75 and the ignition transformer previously mentioned the electrical controls used but not here shown include a warm air temperature limit switch to shut down the burner but not the circulator air motor at a preset upper limit of warm air temperature at the furnace, a fan control to prevent the operation of the circulation air motor if the warm air temperature of the furnace is below a preset temperature and a space thermostat intended to start and stop the oil burner fuel supply motor and solenoid valve as required by the temperature of the space to be heated. Since the construction and control ability of each of these devices are well known in the art and the wiring circuits for any normal use of the various combinations of them are well known in the art, no further description of these instruments and circuits will be here made.

The operation of the burner is as follows. When the space thermostat in the space to be heated experiences a temperature below the desired temperature for which it is set, its contacts close to energize a relay in primary control 75 which then operates to close circuits to energize fuel -supply motor 39 and the operating solenoid of oil delay valve 47.

When motor 39 starts it starts induction `draft fan 40 to pull air into the furnace body 11 through burner head 33 by way of dampered holes 69 in draft tube 35 and air cone 57 and to discharge the gas or air from body 11 through stack 18. At the same time oil pressure is being developed in line 45 by fuel unit 41 and after a preset delay time valve 47 opens to allow oil at full operating pressure into nozzle pipe 48 to be discharged from nozzle 49 into ceramic fire box 38 at a rate and spray form preset by the design of nozzle 49. The oil being cold nozzle 49 discharges oil at a rate greater than its rated oil flow but since the furnace is also cold the air and combustion products handled by fan 40 are also cold and constant speed fan 40 is inducing a greater than normal amount of air through the burner and furnace. Therefore the ratio of lbs. of air to lbs. of oil entering the combustion chamber is maintained at not much over the ratio required for perfect combustion. Then as the furnace heats up the heat reflected from lire box 38 onto nozzle 49 heats up the oil in the nozzle and as the oil heats up the rate of oil spray from the nozzle reduces until its rated flow is reached. A-t the same time that the lire box and nozzle are heating up the furnace body is heating up and the combustion gas temperature at fan 40 is increasing so that while the volume rate of discharge of fan 40 remains approximately constant the weight-oi -air rate of discharge is decreasing to maintain a substantially constant fuelair ratio through the burner.

Having discovered that the fuel-air ratio of the burner throughout both the starting and running period can be held constant within unexpectedly close limits, I next discovered that by giving fan 4G a blade tip speed several times that of the usual forced draft fan used in residential furnaces I would have a condition where I could maintain a substantially constant combustion air pattern in the airf6 oil mixing zone. In the forced draft type of furnace burner, natural draft or barometric pressure differences are relied on to get the combustion gases away from the i furnace and the forced draft burner fan is used merely to supply air as required for combustion. But in many installations the natural draft at starting may be as low as one one-hundredth of an inch, water pressure, which puts sufficient back pressure on the burner at starting that the column of air through the furnace vibrates as in an organ pipe which is not only di-sturbingly noisy but in many cases frightening. After the combustion gases are heated -to the top of the chimney the pressure draft burner will have much more than sufficient air at the same time the oil is warm and in reduced supply.

Thus a second unexpected result was found in the use of my induced draft fan in that by using a `fan with upwards of one inch water pressure capability over its working range l could use around one tenth of that ability to put the air through the furnace and stack and have in the range of nine tenths of an inch pressure to accomplish the dual purpose of stabilizing the rate of air flow into the furnace and increasing the directional stability of the streams of air directed through the air cone into the oil spray closely to control the mixture of air and oil for more perfect combustion.

Then it was discovered that under the average iire box conditions in this work if the air cone was close to and closely parallel the oil spray boundary the air could be ejected from the whirling slots in the expanding air cone at velocities given by pressure drops through the cone of the order of one half inch of water pressure or a median velocity of about 2800 feet per minute. Indeed very` good results have been obtained with air velocities through the cone slots of from 2500 to 3500 feet per minute or over a range of pressure drops across the cone slots of about four tenths of an inch to three quarters of an inch water pressure. Using this much of the fans pressure capability for the stabilized air streams through the air cone slots I retained suicient excess fan pressure to use at the air damper to adjust to the exact air flow required for a particular job.

An important element of this discovery was that with my positive control of the combustion air as described a minimum amount of excess air is required either in starting or running, the air-fuel ratio is stabilized, the air and fuel are completely mixed either in starting or running, the flame is clean and uniform at all times, there is a minimum of burner tiame noise and the highest ef ficiencies ever seen in the operation of commercial oil burner equipment is regularly attained.

Having recited some of the objects of my invention, illustrated and described a preferred form in which my invention may be practiced and explained its operation, I claim:

The combination of an oil fuel furnace having means forming a primary heat radiation space including a combustion chamber open to said primary space, a secondary heat radiation space and an inlet into said combustion chamber for the introduction therethrough of fuel and combustion air into said chamber and said primary space, gas conduit means connecting said primary space with said secondary space, stack means connecting said secondary space with the atmosphere, a cylindrical draft tube having an open end thereof sealed into said inlet opening and means in the series air circuit from atmosphere through said draft tube, said combustion chamber, said primary space, said secondary space and said stack means to said atmosphere for moving combustion air from said atmosphere into -said furnace and products of combustion from said stack means to said atmosphere, and said draft tube including air flow impeding means in said air circuit effective to cause an air pressure drop of at least S tenths of one inch of water pressure thereacross when said furnace is working at its rated capacity, said combination 7 including a pressure atomizing whirling `spray nozzle for distillate oil held coaxially Within said draft tube near its open end `to spray oil therefrom into said combustion chamber and -a nozzle conduit for delivering said oil into said nozzle from a source of `said oil under a required pressure and said means lfor moving air is an air moving fan in said secondary space of said series air circuit, said fan being capable of increasing the gas pressure at its oulet at least one inch of Water pressure over `the gas pressure at its inlet when said furnace is working at its rated capacity.

References Cited in the le of this patent UNITED STAT-ES lPATENTS 'Norton et al Mar. 19, 1929 Koeln Sept. 1, 1936 Nelson Sept. 12, 1939 Stillman Oct. 21, 1941 Mueller Nov. 18, 1941 Logan et al July 18, 1950 

